Tandem rolling mill

ABSTRACT

A tandem rolling mill in which the utilization time of the mill is increased by having one mill stand more than is required for rolling the pass schedules for which the mill is designed. Each mill stand is designed to cover most of the speed range of a preceding mill stand in the rolling line. In operation, the mill stands downstream of a mill stand whose rolls are to be changed or whose rolls were previously changed are set to provide the necessary strip reduction and maintain the normal rolling action of the mill by having their speeds shifted to that of the mill stand upstream thereof. The roll change can then take place without interruption of the rolling.

United States Patent [191 Eibe Oct. 21, 1975 TANDEM ROLLING MILL PrimaryExaminerMilt0n S. Mehr [75] Inventor: Werner W. Eibe, Pittsburgh, Pa. gi Agent or Firmsmith Harding Earley &

0 mer [73] Assignee: Blaw-Knox Foundry & Mill Machinery, Inc.,Pittsburgh, Pa. [57] ABSTRACT [22] Fil d; S t 4, 1974 A tandem rollingmill in which the utilization time of the mill is increased by havingone mill stand more [21] Appl 503056 than is required for rolling thepass schedules for which the mill is designed. Each mill stand isdesigned [52] US. Cl. 72/234; 72/238; 72/249 to cover most of the speedrange of a Preceding mill 51 Int. c1. B21B 1/24; B21B 35/04 stand in therolling line- I operation, the mill stands [58] Field of Search 72/238,239, 234, 249, downstream of a mill stand whose rolls are to be 72/226365 changed or whose rolls were previously changed are set to providethe necessary strip reduction and main- [56] References Cit d tain thenormal rolling action of the mill by having UNITED STATES PATENTS theirspeeds shifted to that of the mill stand upstream 3,331,232 7/1967 King72/250 x .thereof' roll change can take place wlthout 3,754,426 8/1973Adair 72/238 lmerruptlo of the 01mg 11 Claims, 3 Drawing Figures FIG.2.

U.S.'Patent Oct.2I, 1975 Sheet2of2 I I 3,913,368

ENTRY DELIV TOTAL SPD.INTO DELIV. THEOR. COIL GAuGE GAUGE ELONG-IsnsTAND SPEED PRODUC.

IN. IN. ATION ERM. Ema. T/HR.

A .oeo ae .OO74X36 10.81 555 6000 I63 9 .IOOX36 .DII2 use 6.95 572 G000246 C .09o:4a-.o23 4e 3.9I IoaI 4250 476 D .I 87 48 .059 4a 2.?! I2003250 I097 RPM I I I I I I l STAND o I 5 G GEAR RATIO man 15:: o.G:I0.523 MOTOR HP 4000 G000 G000 G000 G000 G000 (zoo/Goo F? m STD 5 CHANGED2 Fl (5 3 STD 4 CHANGED I 2 STD G CHANGED l 2 STD 5 CHANGED I 2 sTD'5 CHNGED I 2 .STD 2 CHANGED l (:9

STD G CHANGED I STD l CHA GED ()9 m ()l m CH G) u u u 01 4 a CD a Q 0: bu b u a Q) TANDEM ROLLING MILL BACKGROUND OF THE INVENTION The inventionrelates to tandem rolling mills and a method of operating the samewhereby the utilization time of the mill is increased.

In the past, tandem rolling mills had downtimes due to porter bar typeroll changing of 15 to 20 percent. The use of rapid roll changersreduces this downtime of the mill up to about one-half or more. However,rapid roll changers still require a downtime of about five minutes.

The utilization time (i.e., the time the mill is actually used) could beincreased another 5 to 6 percent by saving the downtime it takes toperform a rapid roll changing operation. This could bring theutilization time of a tandem cold roll mill to above the 90 percentlevel.

SUMMARY OF THE INVENTION It is the general object of this invention toprovide a tandem rolling mill and a method of operating the same whichincreases the utilization time of the mill by saving the downtimeresulting from a roll changing operaton. This objective is particularlyadvantageous in a fully continuous rolling mill.

Briefly, the general object of this invention is achieved by adding to atandem rolling mill one more mill stand than is required by the mill toachieve the rolling of strip in the pass schedules for which the mill isdesigned. Thus, if a rolling mill requires 5 mill stands to perform therolling of the design pass schedules, the tandem rolling mill of theinvention is provided with 6 mill stands, a prior art four stand coldrolling mill is provided with 5 mill stands, and so on. By reason of theprovision of an additional mill stand, there is always a mill standwhich can be substituted for that mill stand which is to have its rollschanged. More specifically, the mill stands are designed so that eachmill stand can achieve the rolling action of a preceding upstream millstand. To this end, the mill stands are designed such that each canoperate throughout most of the speed range of the adjacent mill stand.Accordingly, a mill stand can be taken out of the rolling line for rollchanging without interrupting the rolling action to any appreciableextent by adjusting the remaining operative mill stands and thesubstitute mill stand to achieve the necessary rolling conditions.

The obvious objection to the concept of adding to a rolling mill a millstand which is unnecessary to rolling the pass schedules for which themill. isdesigned is that it involves a substantial initial investmentand substantially increases the cost of the mill. The additionalinvestment for the extra mill-stand is about 12 to 15% of the totalmechanical and electrical cost of the mill. However, the economies thatare poduced by saving the roll changing time more than offset thisincreased initial cost. With modern high speed rolling mills it isfrequently necessary to change the work rolls several times each shiftbecause of the changing nature of orders available, because of steelanalysis or for any variety of reasons all recognized in the trade.Moreover, the savings are even greater in the case of fully continuousrolling mills because of the higher production involved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of acontinuous rolling mill in accordance with the invention in diagrammaticform;

FIG. 2 is a graph showing a speed cone which illus trates the principlesof the invention; and

FIG. 3 is a chart showing a programmed roll changing procedure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there isshown a fully continuous tandem cold roll mill illustrating theinvention. The mill comprises six mill stands I, 2, 3, 4, 5 and 6 of theconventional four-high type. A three roll bridle unit 18 is locatedadjacent the entry end of mill stand 1 and serves to control the tensionof the strip delivered thereto. Adjacent the bridle unit 18 is a millentry section 20 comprising a pair of payoff reels 22 and 24 and a pairof flatteners 26 and 28. Adjacent the mill entry section 20 is a stripcutting and joining section 30 which comprises a conventional cuttingshear and welder for joining the ends of successive coils to be rolled.From the section 30 the strip is fed to a looper section 32 comprisingthe usual loop cars driven back and forth along tracks to accumulate apredetermined length of strip to deliver strip to the mill standscontinuously while a strip joining operation is performed in the stripcutting and joining section 30 as is conventional in the art. From thelooper section 32 the strip is fed around a roller 34 to the bridle unit18 from which it enters the mill stands.

At the exit end of the mill, the strip is delivered from the mill stand6 to a dividing, shear and tension reel section 40 which comprises apinch roll 42, a shear 44 and a pair of tension reels 46 and 48.Adjacent section 40 is a coil delivery, inspection and strapping section50 which comprises a coil transfer car 52, a circumferential and eyebander 54 and a delivery conveyor 56.

The drive means for each of the mill stands 1, 2, 3, 4, 5 and 6 areindicated at 61, 62, 63, 64, 65 and 66, respectively, and comprise motordriven speed reducers with speed ranges as will be described hereafter.

The automatic roll changing and setting means for each of the millstands 1, 2, 3, 4, 5 and 6 are indicated schematically at 71, 72, 73,74, and 76, respectively, and may take various forms which are wellknown in the art. Such means operate by computer signal to set the rollgap or bite (gauge) and/or effect a roll changing operation.

There is provided a conventional in-line computer of a type presently inuse today for controlling operation of fully continuous rolling mills.The computer 80 controls the entire automatic operation of the rollingmill and controls, for example, the whole mass flow of the rolling mill,the speed, the amount of reduction, and dynamic gauge changes. Thecomputer 80 is arranged to set up each stand for rolling a desired passschedule as is conventional in operational computers for continuousrolling mills in use today. For the purposes of this invention, thecomputer 80 is arranged to control the drive means 61-66 and theautomatic roll changing and setting means 71-76 for the mill stands l-6,respectively, for programmed roll changing, as will be more fullydescribed hereafter.

In the operation of the mill shown in FIG. 1 as a fully continuousrolling mill, the strip is fed from the coil on payoff reel 22 throughthe strip cutting and joining section 30 and the looper 32 and aroundthe roller 34 to the bridle unit 18 from which it enters the mill stand1.

The strip is rolled by five of the six mill stands 1 to 6 which are setby the computer 80 to the proper rolling condition for the pass schedulebeing rolled.

When all of the coil has passed off the reel 22, the trailing end isjoined with the beginning end of a coil on the payoff reel 24. The coilon the payoff reel 24 is passed through the flattener 26 to the stripcutting and joining section 30 where it is joined with the trailing endof the coil just paid off from reel 22. During this end joiningprocedure, which requires that the strip within the strip cutting andjoining section 30 be stopped for a short while, strip is continued tobe fed to the mill stands from the looper section 32 to thereby maintaina continuous supply of strip for rolling. A fully continuous rollingoperation is maintained by alternately supplying coils from the payoffreels 22 and 24 and by joining in the strip cutting and joining section30 the trailing end of the coil being rolled to the beginning end of thenew coil.

Conventional rolling may be performed by delivering strip from a coil onpayoff reel 24 through the flattener 28 and the bridle unit 18 directlyto the mill stand. This alternate is shown by the dashed arrow line inFIG. 1.

At the exit end of the mill, the strip is passed alternately to one ofthe tension reels 46 and 48 whereat the strip is coiled. The rolled coilis then transferred to the circumferential and eye bander 54 by theconveyor 56. From the bander 54, the rolled coil continues to move alongthe delivery conveyor 56 for removal as is conventional in the art. Somecoils are taken at random off conveyor 26 by the coil car 52 forinspection.

In accordance with the invention, the utilization time of the mill isincreased by the addition of one mill stand more than is required forrolling the pass schedules for which the mill is designed. This isillustrated in FIG. 2 which shows a speed cone type of graph as isconventionally used in the art in designing a mill 'for rolling a groupof random pass schedules. On the left vertical side of the graph thereis shown the speed at which the rolls are to be driven in feet perminute. The bottom horizontal line of the graph indicates the entryspeed and the speed at each of the six mill stands at equally spacedlocations. At the bottom of the graph there is also listed the gearratio and the motor horsepower for each of the six mill stands. At thetop of FIG. 2 there is a chart showing the essential conditions of fourrandom pass schedules A, B, C and D. These conditions include the entrygauge, the delivery gauge, the total elongation, the entry speed intothe first mill stand, the delivery speed and the theoretical production.

The pass schedules A to D are shown graphically by indicating the speedat which each of the five mill stands in the rolling line must operateto perform the strip reduction required for that mill stand. Thedesigner of the mill also adds to the graph what is known in the art asa speed cone which comprises the two lines [-1, so as to be certain thateach of the mill stands in the rolling line can be operated at thespeeds required for each of the pass schedules. The lower line I of thespeed cone passes through the minimum or base speeds of the mill stands1 through 6. The upper line I of the speed cone passes through themaximum speeds of the mill stands 1 through 6.

It is noted that the mill stand 1 can operate in a speed range ofbetween 686 and 2058 feet per minute (FPM) which is sufficient to covereach of the speeds required by the pass schedules A through D at theentry end.

This is confirmed by reference to FIG. 2 since these speeds lie betweenthe speed cone I-I. Also, mill stand 5 can operate in a speed range of2050 to 6150 FPM which is sufficient to cover the speeds required by thepass schedules A through D at the delivery end. This is also confirmedby viewing FIG. 2. The speed ranges for each of the mill stands 2, 3 and4 is also sufficient to cover the speeds for each of the pass schedulesA through D as is apparent from FIG. 2.

For example, in pass schedule A the entry speed to mill stand 1 is 555FPM. In accordance with the gauge setting to achieve the desired stripreduction, mill stand 1 is operated at a delivery speed of about 900FPM. Correspondingly, mill stand 2 is operated at a delivery speed ofabout 1600 FPM, mill stand 3 is operated at about 2700 FPM, mill stand 4is operated at about 4175 FPM and mill stand 5 is operated at 6000 FPM.The computer is programmed to perform the gauge settings for each millstand 1 to 6 and control the appropriate drive means 61 to 66 to drivethe mill stands 1 to 6 at the speed corresponding to the gauge settingin accordance with pass schedule A.

It is noted that in accordance with the invention each of the millstands is designed to be driven in a speed range covering most of thespeed range of a preceding mill stand. This is apparent from aconsideration of the graph shown in FIG. 2.

A second speed cone comprising lines II and II is shown in FIG. 2. Thisspeed cone represents the condition when the mill stand 1 is out of therolling line for a roll change and each of the mill stands 2, 3, 4, 5and 6 is shifted to cover the speed of a preceding mill upstreamthereof. This shifting is illustrated in FIG. 2 by the horizontal arrowlines extending from lines II to lines IIII. It will be noted that thespeed cone II--II embraces the pass schedules A through D wherefore thedesign is such that all of these pass schedules can be rolled by anyappropriate combination of the mill stands, i.e., when anyone of themill stands 1 to 6 is taken out of the rolling line for a roll change.

It is noted that the motor speed ranges employed to achieve theabove-described flexibility of rolling is achieved by utilizing a 3 to 1speed range ratio. Equipment of this type is readily available in theart.

FIG. 3 illustrates a typical computer programmed roll change schedule inaccordance with the invention. This schedule takes into account that themill stands near the end of the rolling line are changed more often thanthe front ones, although any variation in the program is possible. Thesequence of roll changing progresses downwardly as viewed in FIG. 3.Thus, in the upper row there is illustrated what occurs when the millstand 6 has its rolls changed. In this case mill stands 1 through 5 areactive while the rolls for mill stand 6 are changed. The mill stands 1through 5 are, of course, set for the speed indicated by the passschedule such as those shown at A through D in FIG. 2.

The next row illustrates what occurs when the rolls for mill stand 5 arechanged. In this case, mill stands 1 through 4 remain active at theirprevious setting while stand 6 is reset to take over the rolling actionof the stand 5. This mode of operation is illustrated in FIG. 1.

The next row illustrates what occurs when mill stand 4 is changed. Inthis case, stands 1, 2, 3 and 5 remain active at their previous settingand mill stand 5 is set to take over the rolling action of mill stand 4.

The next row illustrates the changing of mill stand 6 again in whichcase mill stands I through 5 perform the rolling operation in accordancewith the pass schedule.

The next row illustrates what occurs when mill stand 3 is changed. Inthis case, stands I and 2 remain active at their previous setting andmill stands 4, 5 and 6 are reset to take over the rolling action of millstands 3, 4 and 5, respectively.

The next line illustrates what occurs when mill stand 5 is changed andthis is described above.

The next line illustrates what occurs when mill stand 2 is changed. Inthis case, stands 1 and 6 remain active at their previous setting andmill stands 3, 4 and 5 are set to take over the rolling action of millstands 2, 3 and 4, respectively.

The next line illustrates what occurs when mill stand 6 is changed andthis was described above.

The last line illustrates what occurs when mill stand 1 is changed. Inthis case the mill stands 2, 3, 4, 5 and 6 are reset to take over therolling action of mill stands 1, 2, 3, 4 and 5, respectively. Thiscorresponds with FIG. 2 wherein the entire speed cone appears to beshifted to the left.

The roll changing program then continues back with a roll change formill stand 6 as illustrated in the top row of the chart shown in FIG. 3and is continuously repeated under the control of the computer 80 in theprogression indicated on this chart.

The entire program is under the control of the computer 80 which setsthe drive means 61 through 66 and actuates the roll changing and settingmeans 71 through 76 to achieve the sequence of operation set in theprogram. In operation, the computer 80 controls the bite of the standssuch that while the mill stand which requires roll changing is havingits rolls withdrawn from contact with the strip, the gauge and speed ofstands downstream of the stand being changed or the stand previouslychanged are set to take over the rolling action of the stand upstreamthereof. After the computer 80 has completed the changes in roll bite(or gauge), the rolls to be changed can be removed whenever it isconvenient without affecting the production. During the time that thecomputer 80 is directing the changes in roll bite, the strip can bemoved slowly or it can be stopped momentarily. However, this involvesvery little or no loss of strip or reduction in the production of themill.

It will be apparent that by the above described tandem rolling milldesign and method of operating the mill, the utilization time of themill is increased, since the roll change can take place withoutinterrupting the rolling to any appreciable extent. The design inaccordance with the invention saves the downtime it takes to perform theroll changing operation and can thus bring the utilization time of atandem cold roll mill to above the 90 percent level.

I claim:

1. A tandem rolling mill comprising:

a plurality of mill stands arranged in tandem in a rolling line forsuccessively rolling a strip of material to reduce the thicknessthereofa desired amount in a single pass through said mill stands,

said plurality of mill stands being adapted to roll strip in accordancewith a predetermined group of pass schedules so designed that all passesof each schedule are required to produce said desired strip reduction,

an additional mill stand added to said plurality of mill stands andarranged in said rolling line,

and independent drive means for each of said mill stands in said rollingline,

the drive means for each mill stand having a speed range covering mostof the speed range of the drive means for a mill stand immediatelyupstream thereof and a maximum speed greater than the maximum speed ofthe drive means for a mill stand immediately upstream thereof.

2. A rolling mill according to claim 1 including means for controllingsaid drive means to operate all of said mill stands except one in anycombination of mill stands to roll strip in accordance with said groupof pass schedules.

3. A rolling mill according to claim 2 including means for changing therolls of each of said mill stands, and means for controlling said drivemeans and said roll changing means in a programmed sequence so that theroll changing means for each mill stand and a corresponding drive meansis out of operation a predetermined sequence.

4. A rolling mill according to claim 1 wherein the speed cone of saiddrive means for said first-mentioned plurality of mill stands enclosesthe group of pass schedules for which the rolling mill is designed andthe speed cone for any combination of mill stands minus one alsoencloses said group of pass schedules.

5. The method of operating a tandem rolling mill having a plurality ofmill stands arranged in a rolling line for successively rolling strip toreduce the thickness thereof to a desired thickness in a single passthrough said mill stands in accordance with a group of pass schedulesfor which the mill is designed, and a mill stand added to the firstgroup of mill stands and arranged in the rolling line, each of said millstands being independently driven and capable of operating in most ofthe speed range of and at a higher maximum speed than a mill standimmediately upstream in said rolling line, comprising the steps of:

rolling a strip of material by the operation of only said first group ofmill stands which are set to operate at successive desired speeds androll bits in accordance with a pass schedule to achieve the desiredstrip reduction,

adding said additional mill stand to the rolling line and removing oneof said first group of mills from the rolling line,

and operating all of the remaining mill stands in said rolling line atthe successive speed and roll bite settings used during saidfirst-mentioned strip rolling operation.

6. The method according to claim 5 in which the mill stand removed fromrolling line has its rolls changed while the remaining rolls areoperated to roll strip.

7. The method according to claim 6 in which all of said mill stands areautomatically removed from the rolling line one at a time for a rollchange in accordance with a programmed sequence of operation under thecontrol of a computer.

8. The method according to claim 7 wherein there are at least four millstands in said first group capable of rolling strip in accordance withsaid design pass schedules for the mill.

9. The method according to claim 7 wherein the computer completes thechanges in roll bite and speed for the mill stands downstream of the onebeing taken out of the rolling line prior to the roll changing operationof the mill stand taken out of the rolling line.

10. The method of operating a rolling mill according to claim in whichstrip to be rolled is fed continuously to the rolling line and rolledstrip is delivered continuously from said rolling line so as to operatethe rolling mill as a fully continuous mill.

11. A fully continuous rolling mill comprising:

a plurality of mill stands arranged in tandem in a rolling line forsuccessively rolling a strip of material to reduce the thickness thereofto a desired thick ness in a single pass through said mill stands,

said plurality of mill stands being adapted toroll strip in accordancewith a predetermined group of pass schedules so designed that all passesof each schedule are required to produce the desired strip reduction, I

means at the entry end of the rolling line for delivering strip to berolled continuously to said mill stands, and means at the exit end ofthe rolling line for continuously receiving rolled strip.

1. A tandem rolling mill comprising: a plurality of mill stands arrangedin tandem in a rolling line for successively rolling a strip of materialto reduce the thickness thereof a desired amount in a single passthrough said mill stands, said plurality of mill stands being adapted toroll strip in accordance with a predetermined group of pass schedules sodesigned that all passes of each schedule are required to produce saiddesired strip reduction, an additional mill stand added to saidplurality of mill stands and arranged in said rolling line, andindependent drive means for each of said mill stands in said rollingline, the drive means for each mill stand having a speed range coveringmost of the speed range of the drive means for a mill stand immediatelyupstream thereof and a maximum speed greater than the maximum speed ofthe drive means for a mill stand immediately upstream thereof.
 2. Arolling mill according to claim 1 including means for controlling saiddrive means to operate all of said mill stands except one in anycombination of mill stands to roll strip in accordance with said groupof pass schedules.
 3. A rolling mill according to claim 2 includingmeans for changing the rolls of each of said mill stands, and means forcontrolling said drive means and said roll changing means in aprogrammed sequence so that the roll changing means for each mill standand a corresponding drive means is out of operation a predeterminedsequence.
 4. A rolling mill according to claim 1 wherein the speed coneof said drive means for said first-mentioned plurality of mill standsencloses the group of pass schedules for which the rolling mill isdesigned and the speed cone for any combination of mill stands minus onealso encloses said group of pass schedules.
 5. The method of operating atandem rolling mill having a plurality of mill stands arranged in arolling line for successively rolling strip to reduce the thicknessthereof to a desired thickness in a single pass through said mill standsin accordance with a group of pass schedules for which the mill isdesigned, and a mill stand added to the first group of mill stands andarranged in the rolling line, each of said mill stands beingindependently driven and capable of operating in most of the speed rangeof and at a higher maximum speed than a mill stand immediately upstreamin said rolling line, comprising the steps of: rolling a strip ofmaterial by the operation of only said first group of mill stands whichare set to operate at successive desired speeds and roll bits inaccordance with a pass schedule to achieve the desired strip reduction,adding said additional mill stand to the rolling line and removing oneof said first group of mills from the rolling line, and operating all ofthe remaining mill stands in said rolling line at the successive speedand roll bite settings used during said first-mentioned strip rollingoperation.
 6. The method according to claim 5 in which the mill standremoved from rolling line has its rolls changed while the remainingrolls are operated to roll strip.
 7. The method according to claim 6 inwhich all of said mill stands are automatically removed from the rollingline one at a time for a roll change in accordance with a programmedsequence of operation under the control of a computer.
 8. The methodaccording to claim 7 wherein there are at least four mill stands in saidfirst group capable of rolling strip in accordance with said design passschedules for the mill.
 9. The method according to claim 7 wherein thecomputer completes the changes in roll bite and speed for the millstands downstream of the one being taken out of the rolling line priorto the roll changing operation of the mill stand taken out of therolling line.
 10. The method of operating a rolling mill according toclaim 5 in which strip to be rolled is fed continuously to the rollingline and rolled strip is delivered continuously from said rolling lineso as to operate the rolling mill as a fully continuous mill.
 11. Afully continuous rolling mill comprising: a plurality of mill standsarranged in tandem in a rolling line for successively rolling a strip ofmaterial to reduce the thickness thereof to a desired thickness in asingle pass through said mill stands, said plurality of mill standsbeing adapted to roll strip in accordance with a predetermined group ofpass schedules so designed that all passes of each schedule are requiredto produce the desired strip reduction, an additional mill stand addedto said plurality of mill stands and arranged in said rolling line,independent drive means for each of said mill stands in said rollingline, the drive means for each mill stand having a speed range coveringmost of the speed range of the drive means for a mill stand immediatelyupstream thereof and a maximum speed greater than the maximum speed ofthe drive means for a mill stand immediately upstream thereof, means atthe entry end of the rolling line for delivering strip to be rolledcontinuously to said mill stands, and means at the exit end of therolling line for continuously receiving rolled strip.